280i USA Spec - de-catting

[Gav T]

Hi all

Want to de-cat my 280i. The smog police don't patrol South Dakota. The bible says that if you do this you need to get a new ECU as the injection system on US spec cars was a closed loop system. Euro spec cars had an open loop system as I understand. If I just go ahead and remove the cats will this really muck things up?. I can't see how as all it will do is let the engine breath better.

Any one have any thoughts?

Cheers

Gavin
1986 280i S2 - USA spec

[TXcoyote]

As difficult as it is to keep that K-Jetronic running well I wouldn't trash the CAT. What I would do was what I did with mine; replaced the exhaust with a true dual system with twin Cats mounted under the floorboards and not under the oilpan so it can bake the motor oil. Just be sure to put shielding. It will help with the power and mine sounded great. Check out the US TVR club for more info.

[leorest]

Shirley the sensor after the cat can be replaced with a resistor value or link to fool the ecu into thinking the cat is AOK?

Otherwise an upgrade to EFI controlled by Megersquirt would give cost effective $/BHP.

... and don't call me Shirley.

[GreenV8S]

leorest said:

Shirley the sensor after the cat can be replaced with a resistor value or link to fool the ecu into thinking the cat is AOK?

What sensor's that?

[taimar78]

Who is "Shirley the Sensor"?

[leorest]

GreenV8S said:

leorest said:

Shirley the sensor after the cat can be replaced with a resistor value or link to fool the ecu into thinking the cat is AOK?

What sensor's that?

In which case there shouldn't be a problem removing the cat?

[TXcoyote]

Or do what I'm doing and bag the lot and install a Rover V8

[TVRleigh]

There should be a sensor on the exhaust somwhere, when the car in running ok take it off and quicky connect a ohm meter on the connector,

then get a reister of this value and fit it to conector, and see if car runs fine with out it.

Hopfull its like most sensors and just changes resistance.

[adam quantrill]

This might work short-term (i.e. while the engine is still warm) but I can't see this working for the full range of operating conditions. I think you'll have to swap the ECU over to open-loop.

[Gav T]

TXcoyote said:

What I would do was replaced the exhaust with a true dual system with twin Cats mounted under the floorboards and not under the oilpan so it can bake the motor oil. Just be sure to put shielding. It will help with the power and mine sounded great. Check out the US TVR club for more info.

This mod was already done by the previous owner, he had a Benny Wu system fitted. The cat under the driver's seat is shot - sounds like a tin can with a load of nails in it. From the sound of it, it seems that just changing the cat will be the simplist and cheapest route. Even with the cats relocated and a true twin pipe system the car is still somewhat sluggish. I was hoping just to breath a little more fire into it by dumping the cats. I might as well change out the rear canisters as well as these are quite chunky and the car is not that loud. I think I just need to make everything a little more free flowing. Thanks all.

Gavin
1986 280i S2 USA

[TVRleigh]

Just put a V8 in it

[adam quantrill]

Hang on a minute:

Gav T said:

The bible says that if you do this you need to get a new ECU as the injection system on US spec cars was a closed loop system.

Where is the lambda sensor - isn't it before the cats anyway? In which case, what difference will it make if the cats are replaced with straight-through pipe (or just poke out the remaining catalyst honeycomb)?

It should run fine.

[350zwelgje]

adam quantrill said:

Hang on a minute:

Gav T said:

The bible says that if you do this you need to get a new ECU as the injection system on US spec cars was a closed loop system.

Where is the lambda sensor - isn't it before the cats anyway? In which case, what difference will it make if the cats are replaced with straight-through pipe (or just poke out the remaining catalyst honeycomb)?

It should run fine.

Was just now thinking the same and read your post Adam. But it will only release power based on better exhaust flow, and not from the engine as lambda 1 isn't best for power. Could be a good first step, but ECU & exhaust gas recycling setup still needs fettling/replacement to release the rest.

Rob

[Grady]

My CAT was removed by the prior owner and I don't think anything else was changed and it ran fine.

Then to comply with the local smog rules I added two new "sport" CATs - but on bad advice - too far aft (near the rear wheels) where they don't get hot enough to do any good. They quieted it down a bit but it still runs fine.

Might be best to remove and see what happens. If it runs badly, you can always replace the CAT or figure out how to make an upgrade. Grady

[tvr-280i]

I did the same to my 280i and all that you need to do is remount to oxygen sensor in the exhaust. Put it close to it's original position. It will run great with no other mods needed. Have fun.

[tvr-280i]

Consider swapping exhaust manifolds side to side so that they point to the rear for better flow now that you don't need a cat under the oil pan.

[Grady]

tvr-280i said:

Consider swapping exhaust manifolds side to side so that they point to the rear for better flow now that you don't need a cat under the oil pan.

Good plan... but use the opportunity to remote mount the oil filter up front. Before I moved the filter, I would buy the shortest filter I could locate and still had to drop the passenger side exhaust at the manifold flange to get the old filter out and the new in. Grady

[Gav T]

adam quantrill said:

Hang on a minute:

Gav T said:

The bible says that if you do this you need to get a new ECU as the injection system on US spec cars was a closed loop system.

Where is the lambda sensor - isn't it before the cats anyway? In which case, what difference will it make if the cats are replaced with straight-through pipe (or just poke out the remaining catalyst honeycomb)?

It should run fine.

thats what I thought, but what I read did make be think. I'll just put the straight pipe in and see what happens. If it screws things up then I'll go to plan B.

tvr-280i said:

Consider swapping exhaust manifolds side to side so that they point to the rear for better flow now that you don't need a cat under the oil pan.

As the system has already been modified by Benny Wu (I have no idea who he is but the guy I got the car from made a big deal about the Benny Wu exhaust ) swaping the exhaust manifolds may have already been done. I'll check.

Grady said:

but use the opportunity to remote mount the oil filter up front. Before I moved the filter, I would buy the shortest filter I could locate and still had to drop the passenger side exhaust at the manifold flange to get the old filter out and the new in. Grady

Changing the oil is also on my list. I'll see how hard it is to get at. If it's a bugger I'll look into relocationg it. You wouldn't have a photo of where you mounted yours would you?

thanks for all the help - Gavin